This invention relates to the field of motor graders and, more particularly, to an attachment that adapts such machines for laying down, in one pass, a finished layer of aggregate material such as base rock or cold mix asphalt onto roads, streets, parking lots or driveways.
The known method of laying down base rock or cold mix asphalt involves a two-step operation in which the material is first dumped from a truck onto the ground or roadbed. A motor grader then comes along and spreads the material back and forth using its moldboard until the material is at the desired depth, width and slope. Typically, excess material slips into ditches on either side of the roadbed and is wasted. Significant, time-consuming working and reworking of the material may be necessary in order to achieve the desired depth, width and crown of the roadbed, which not only slows the overall process but also increases the likelihood of wasting significant amounts of material. Moreover, excessive handling and manipulation of base rock material can result in the limestone fines becoming separated from the aggregate and settling to the bottom of the layer, detracting from their ability to solidify when wet and hold the aggregate in a solid matrix that provides a better roadbed. Generally speaking, the less handling the better when laying down gravel material.
The present invention converts a motor grader into a machine that is capable of laying down in one pass a finished layer of aggregate material such as base rock or asphalt that has the desired thickness, width and profile of the finished product. By laying down the finished product on-the-go in a one-pass operation, significant time and labor savings can be achieved, as well as better control. Furthermore, less handling means a better quality roadbed where base rock is the material being deposited.
The present invention contemplates attaching a special distribution hopper to the front end of the motor grader ahead of the front wheels and a special screed to the moldboard behind the front wheels. As the motor grader advances, the hopper continuously receives material from a dump truck being pushed along the roadbed ahead of the grader by the hopper, and such material is continuously metered out onto the roadbed or other surface to form a swath located between the front wheels. The discharged swath of materials is then acted upon by the trailing screed, which skims off excess material from the top of the swath and spreads it laterally outwardly in opposite directions to produce a layer that is wider than the front wheels. Outermost shields at opposite left and right ends of the screed limit the width of the outwardly spreading materials to prevent spillage into ditches alongside the roadbed. The screed is mounted on the front side of the moldboard so as to be in a position to engage and work the materials instead of the moldboard. However, since the moldboard is adjustable in a variety of directions through various hydraulic actuators on the grader, manipulation and adjustment of the moldboard by the actuators can be used to correspondingly adjust the screed. Because the screed is pointed with a pair of diverging wings, adjustment of the nose of the screed upwardly or downwardly relative to the rear ends of the wings results in changes in the shape of the crown that is on the layer of materials being deposited and spread. In one preferred embodiment of the invention, such crown can range from a six inch negative crown to a flat or level crown and to a six inch positive crown at the other extreme.
The two wings of the screed can be extended and retracted hydraulically from the seat of the motor grader so as to correspondingly adjust the width of the material being laid down. The discharge outlet at the bottom of the distribution hopper has of a pair of side-by-side metering gates that can be independently adjusted so as to correspondingly vary the rate of discharge from the hopper. An operator""s platform is provided on the backside of the distribution hopper to enable an extra worker to ride the machine at that location and operate controls for the metering gates as he observes loading and discharging of the hopper. A rotary agitator inside the hopper helps assure an orderly and even discharge flow from the hopper.